Japanese Unexamined Patent Application Publication No. 2010-170255 attempts to enable lane boundary lines to be detected with high precision in a lane boundary line detection device that detects lane boundary lines, which are boundaries of driving lanes in which a vehicle drives, from captured images ([0005], Abstract).
In Japanese Unexamined Patent Application Publication No. 2010-170255 (Abstract), departure warning processing performed when detecting lane boundary lines computes a degree of certainty representing a probability that the lane boundary line candidate is a lane boundary line based on the shape of each lane boundary line candidate, for lane boundary line candidates representing plural edge components running along the driving direction of the vehicle in the captured images (S320). Degree of certainties corresponding to lane boundary line candidates in the vicinity of a position of a leading vehicle, which represents a vehicle driving ahead of the vehicle, are then changed to higher values (S330, S340), and the lane boundary line candidate corresponding to the highest degree of certainty is identified as the lane boundary line (S380).
Determination as to whether or not a lane boundary line candidate is in the vicinity of the position of the leading vehicle (or a degree of certainty PPi based on this) is made based on the distance (an end section distance) between the lane boundary line candidate and either a left or right end section of the leading vehicle (the end section at the side closest to the lane boundary line candidate) (FIG. 5(b), [0042], [0043]).
As described above, the distance (end section distance) between the lane boundary line candidate and either the left or right end section of the leading vehicle (the end section at the side closest to the lane boundary line candidate) is employed in Japanese Unexamined Patent Application Publication No. 2010-170255 (FIG. 5(b), [0042], [0043]). In other words, a left lane boundary line is compared against a left end section of the leading vehicle, and a right lane boundary line is compared against a right end section of the leading vehicle, to make separate determinations of the left and right lane boundary lines in Japanese Unexamined Patent Application Publication No. 2010-170255.
Thus, a correct combination is sometimes not obtained in Japanese Unexamined Patent Application Publication No. 2010-170255. For example, when left and right lane boundary lines are determined separately, in cases in which erasure of old white lines was forgotten or there are remaining road repair markings or braking marks, there is a possibility that old white lines in positions that happen to have high reliability could be picked up. Moreover, in cases in which the technology of Japanese Unexamined Patent Application Publication No. 2010-170255 is employed during a traffic jam, the leading vehicle will be close to the vehicle, shortening the length of the white line that can be subject to recognition and lowering the recognition precision.